The present application relates to an infrared signal receiver, a liquid crystal display, and an optical element applicable thereto, capable of suppressing degradation of sensitivity to remote controllers of video display devices such as liquid crystal display and its peripheral instruments, caused by near infrared radiation emitted, for example, from the liquid crystal display.
Today's video display is diversified into several categories including cathode ray tube display, plasma display, liquid crystal display and so forth. Almost all of these video displays are given with remote operating units, that is, remote controllers making use of near infrared communication. Signal wavelength of a general remote controller, and a sensitivity curve of its photo-detector unit are shown in FIG. 13. The signal wavelength of the remote controller shows a single peak having the center at 940 nm, and a half-value width of 50 nm or around. On the other hand, the photo-detector unit has sensitivity over a broad range from 850 nm to 1150 nm.
Under the environment such that near infrared radiation other than that of the remote controller signal also exists, in addition to the remote controller signal, in the wavelength region in which the photo-detector unit shows its sensitivity, sensitivity of communication with the remote controller will degrade, and distance allowing communication between the remote controller and the main unit of communication instrument will be reduced. In particular, plasma display is known to emit a huge energy of near infrared radiation which is causative of degradation in sensitivity to remote controllers of infrared communication instruments (for example, portable handset of telephone set, air conditioner, optical disc drive, etc.) placed at around the display.
As a countermeasure therefor, it has been known that provision of an optical filter containing a dye capable of absorbing light having wavelength in the near infrared region, in front of the display is effective (see Japanese Patent Application Publication (KOKAI) No. 2005-272660 (Patent Document 1), for example). Most of current plasma displays adopt this sort of optical filter.
Japanese Patent Application Publication (KOKAI) No. 2006-41657 (Patent Document 2) discloses a configuration such that an optical filter intercepting a predetermined wavelength of light emitted from the plasma display is provided to the photo-detector unit of the remote controller, in order to suppress influences of the predetermined wavelength of light in the near infrared region emitted from the plasma display exerted on the infrared communication. Considering now that the peak wavelength of infrared radiation emitted from the plasma display resides in the range from 825 nm and 880 nm, the optical filter is configured as characteristically showing a transmittance of light of 80% or more in the wavelength region longer than 900 nm, reducing the transmittance of light in the range from 900 nm to 800 nm, and showing a transmittance of light of nearly 0% in the wavelength region shorter than 800 nm.
By the way, also liquid crystal display, besides the plasma display, has emerged as a flat screen television set, and has been becoming the main stream of recent large-sized television sets. Recent trend in increase in screen size of the liquid crystal display causes gradual increase also in the energy of near infrared radiation emitted from the back light, while being still in a level lower than the plasma display. FIG. 14 shows an emission spectrum of the liquid crystal display in the near infrared region.
A known method of intercepting the near infrared radiation emitted from the back light of the liquid crystal display is such as providing a dye-containing filter on the display side, similarly to as in the plasma display. The near infrared absorbing dye, however, generally shows a slight absorption also in the visible light region, and therefore lowers luminance of displayed video image. For the liquid crystal television set, allowed for only a narrower range of luminance as compared with plasma television set, it is very difficult to compensate the loss of luminance caused by absorption by the filter, with the aid of output of the back light or the like.
On the other hand, another possible method is such as disposing, at the photo-detector unit of the remote controller, an optical filter capable of intercepting a predetermined wavelength of near infrared radiation emitted from the display, as disclosed in Patent Document 2. However, unlike the infrared radiation emitted from the plasma display, the infrared radiation emitted from the liquid crystal display shows a peak wavelength at 911 nm, 922 nm, 965 nm and 1,013 nm as shown in FIG. 14. As a consequence, even use of the above-described optical filter having a transmittance of light, longer than 900 nm, of 80% or more cannot provide a countermeasure against infrared radiation emitted from the liquid crystal display.